A unilateral circuit model, which precisely predicts small signal response over a wide range of frequencies and bias points, is quantitatively analyzed and presented. The shortfall of current unilateral assumption and transformation technique is presented. A complete and explicit analysis is provided to develop a compact unilateral circuit model. The model is intended to predict input reflection, forward transmission and output reflection coefficients over wide range of frequencies. The technique is validated by transforming bilateral a small signal model of 3 x 3 μm x 40 μm, InGaP/GaAs HBT into its unilateral equivalent over the frequency range of 250 MHz to 30 GHz. The accuracy of the technique is corroborated at various bias conditions; collector current from 3 mA to 150 mA and collector-emitter voltage from 1 V to 5 V. Simulated results show very good agreement between small signal responses of transformed unilateral and bilateral circuit models.

In this paper, the problem of target detection in co-located ``multi-input multi-output" (MIMO) radars is considered. A pulse-train signaling is assumed to be used in this system. As the doppler effect should be considered for the pulse-train signaling, we are confronted by a compound hypothesis testing problem, so in this paper a Generalized Likelihood Ratio (GLR) detector is derived. The high complexity of this detector makes us derive a new detector based on the theory of Independent Component Analysis (ICA). It is shown that the computational load of the ICA-based detector is much less than the GLR detector. It is also shown that the sensitivity of the ICA-based detector to the doppler effect is very low. According to this approach, an appropriate signal design method is presented, based on the separation performance of the ICA algorithms. It is shown that independent random sequences are proper signals in the sense of detection performance.

Compressed sensing (CS) is a new technology for recovering sparse data from undersampled measurements. It shows great potential to reduce energy for sensor networks. First, a basic global superposition model is proposed to obtain the measurements of sensor data, where a sampling matrix is modeled as the channel impulse response (CIR) matrix while the sparsifying matrix is expressed as the distributed wavelet transform (DWT). However, both the sampling and sparsifying matrixes depend on the location of sensors, so this model is highly coherent. This violates the assumption of CS and easily produces high data recovery error. In this paper, in order to reduce the coherence, we propose to control the transmit power of some nodes with the help of t-average-mutual-coherence, and recovery quality are greatly improved. Finally, to make the approach more realistic and energy-efficient, the CIR superposition is restricted in local clusters. Two key parameters, the radius of power control region and the radius of local clusters, are optimized based on the coherence and resource consideration in sensor networks. Simulation results demonstrate that the proposed scheme provides a high recovery quality for networked data and verify that t-average-mutual-coherence is a good criterion for optimizing the performance of CS in our scenario.

Two probe-compensated near-field-far-field transformations with spherical spiral scanning tailored for antennas having two of their dimensions very different from the third one are developed by properly applying the unified theory of spiral scans for nonspherical antennas. One is suitable for electrically long antennas, which are considered as enclosed in a cylinder ended in two half-spheres. The other adopts a surface formed by two circular ``bowls'' with the same aperture diameter but different lateral bends to shape a quasi-planar antenna. These flexible modelings fit very well many actual antennas by properly setting their geometric parameters. Great reduction of the number of data to be acquired is achieved, thus significantly reducing the required measurement time. Numerical tests validating the accuracy of the proposed techniques and their stability with respect to random errors affecting the data are shown.

A novel method allowing the ultrafast scanning of an area thanks to an Ultra Wide Band (UWB) antenna array is proposed in this paper. This method is based on the use of asynchronous optical pulses trains with different repetition rates obtained in amplified regenerative cavities. By means of optoelectronic switching, providing short powerful electrical pulses trains to an UWB antenna array, it is possible to spatially scan a large area in less than 1 ms. The paper presents the principle of the transient beam steering and its potentialities to realize an ultrafast detection system.

In this paper, a modified planar balanced Vivaldi antenna with endfire characteristics near the metal surface is proposed for 6-18 GHz applications. The proposed antenna structure consists of three copper layers, among which two external layers locate on the two outsides of two dielectric substrates, and the central layer is sandwiched by these two dielectric substrates. To further enhance the end-fire radiation characteristic, a number of novel techniques are proposed, including elongation and shaping of the supporting substrate of a conventional balanced antipodal Vivaldi antenna beyond its aperture, using an I-shaped slot loaded radiation patch and cutting a triangle on the edge of three copper layers. Measured and simulated results show that the proposed antenna not only exhibits good impedance bandwidth, but also improves the end-fire performance in the operational frequency of 6-10 GHz and achieves high gain in the end-fire direction, low cross-polarization and high front-to-back (F-to-B) ratio.

The diffraction problem of a three-dimensional elliptic Gaussian beam on a aperture array of rectangular holes is solved. The both normal and oblique incidences of the beam are considered and the results are presented in the form of the three-dimensional patterns. The pattern lobe distortion and conditions at which the side lobes appear are studied. The conditions under which the shift of the reflected and transmitted field patterns appears are studied. The existence of higher spatial Floquet harmonics in the case of oblique beam incidence is observed.

The objective of this paper is to study the wideband characteristics of the radio channel in a tunnel environment, not only the delay spread, but also the angle of departure/arrival of the rays, their relative weights and their delays, which are important values for Multiple-Input Multiple-Output applications. In order to achieve this goal, a measurement campaign has been carried out in a straight arched tunnel over a frequency band extending from 2.8 to 5.0 GHz and distance varying from 50 m up to 500 m. First, the variations of the channel impulse response and of the delay spread versus the distance between the transmitter and the receiver are analyzed. Then, the bidirectional channel characteristics have been extracted from the measured channel matrices using a high resolution estimation algorithm. The main contribution of this paper is to clearly show the quantitative variation of the delay spread and the angle of departure/arrival of the rays along a real tunnel and to investigate the possibility of using the ray theory in a rectangular tunnel to interpret experimental results obtained in an arched tunnel.

Finding sparsifying transforms is an important prerequisite of compressed sensing (CS) theory. It is directly related to the reconstruction accuracy. In this work, we propose a new dictionary learning (DL) algorithm to improve the accuracy of CS reconstruction. In the proposed algorithm, Least Angle Regression (LARS) algorithm and an approximate SVD method (ASVD) are respectively used in the two stages. In addition, adaptive sparsity constraint is used in the sparse representation stage, to obtain sparser representation coefficient, which further improves the dictionary update stage. With these data-driven adaptive dictionaries as sparsifying transforms for image compressed sensing, results of experiments demonstrate noteworthy outperformance in peak signal-to-noisy ratio (PSNR), compared to CS based on dictionaries learned by K-SVD, in the sampling rate of 0.2-0.5. Besides, visual appearance of reconstruction detail at low sampling rate improves, for reducing of `block' effect.

In this paper, the interaction of a planar inverted-F antennas array, mounted on a mobile handset, with a human hand-head phantom is investigated in the 1.9 GHz band. The hybrid approach involving the particle swarm optimization (PSO) and Nelder-Mead (NM) algorithm is considered to optimize the complex excitations of the adaptive array elements in a mutual coupling environment for different beamforming synthesis. Firstly, the effect of the human hand-head on the handset radiation characteristics is studied. Then, the spatial-peak specific absorption rate (SAR) values of 2- and 4-element PIFA arrays for mobile handset in the vicinity of a human hand-head are evaluated numerically for different scenarios. The antenna is analyzed completely using finite difference time domain (FDTD) method while the interaction is performed using the CST Microwave Studio software.

We investigate analytically the asymptotic behavior of high-order spurious prolate spheroidal modes induced by a second-order local approximate DtN absorbing boundary condition (DtN2) when employed for solving high-frequency acoustic scattering problems. We prove that these reflected modes decay exponentially in the high frequency regime. This theoretical result demonstrates the great potential of the considered absorbing boundary condition for solving efficiently exterior high-frequency Helmholtz problems. In addition, this exponential decay proves the superiority of DtN2 over the widely used Bayliss-Gunsburger-Turkel absorbing boundary condition.

The EM analysis of double-layered thick FSS structure with low-loss dielectric medium between the FSS layers has been carried out using MM-GSM technique. In this analysis, both evanescent and propagating modes are included that enhances the accuracy of the computation. This method provides less computational complexity in the formulation of FSS structures as compared to other numerical techniques. The cascaded FSS structure shows bandpass response (>95% transmission) over a frequency range from 8.84 GHz to 10.74 GHz. It is found that this FSS structure shows very good in-band transmission characteristics and excellent roll-off characteristics outside the band. Further, the dependence of transmission characteristics on the spacing between the FSS layers is also investigated. The optimum bandpass response is achieved for 0.3λ spacing between the layers. This FSS structure offers superior bandpass response and structural rigidity required for airborne radome applications.

A compact microstrip-line dual-band bandpass filter with controllable characteristics is presented using a stub-loaded resonator. The resonator is formed by loading one open circuit terminated stub in shunt to a simple uniform impedance line. The passband frequencies of the dual-band filter can be conveniently controlled by tuning the lengths of stub-loaded resonators. The bandwidth of the first passband can be controlled by tuning the parameters of center stub-loaded resonator, and the bandwidth of the second passband is determined by the coupling between the sideward stub-loaded resonators. To illustrate the concept, a second-order dual-band filter is designed, fabricated and measured. Simulated and measured results are found in good agreement with each other.

A new method for increasing the bandwidth (BW) of a class of cloaks is presented. Simulation results reveal that the bandwidth of this class of cloaks is increased by embedding the two-dimensional transmission networks in a medium whose refractive index is smaller than unity. The low refractive index medium is realized by embedding several thin wires in a host medium. The overall bandwidth of the proposed cloak for reflectance less than -25 dB is revealed to be increased by more than 17% compared to its conventional counterpart.

The present work is motivated by our recent experimental results [2-4] that indicate on anomalously small retardation of bound (or velocity-dependent) electromagnetic (EM) fields in the near zone of an emitter, whereas in the far zone the retardation tends to the standard value determined by the velocity of light c. Such anomaly is specific only for bound field component, while EM radiation has the constant propagation velocity c in the entire space. One possible explanation of these experimental results can be linked to our earlier finding [6, 8] that conventional EM energy-momentum (EMEM) tensor describes bound and radiative EM fields only in spatial regions free of charges and currents. In this work we show that an additional term has to be included into the standard EMEM tensor in order to make viable the description of the whole system of ``charges plus fields". Such approach to the EMEM tensor actually admits anomalously small retardation of bound EM fields in regions very close to a field source, providing the standard propagation in the far zone. Some special implications are also discussed.

This paper develops a practical receiver suggested for cooperative systems using decode-and-forward transmission and compares it to the theoretical sub-optimum λ-MRC receiver model. The proposed receiver model adopts a channel blind λ-combiner and employs a practical estimation of the combiner's weight λ that changes adaptively for each received bit. The λ estimation process relies on a dynamic-blind calculation performed on the incoming bit stream using an approximate formula. The accuracy of the estimated values of λ against the numerical (optimum) values is verified by comparing their effects on the performance curves. Next, the performance of the proposed receiver is evaluated against the sub-optimum receiver using the closed-form performance equations then verified using an actual implementation of the decode-and-forward cooperative algorithm. The use of the proposed receiver is shown to have reliable performance under different channel assignments and provides adaptivity to channel variations without complexity or exaggerated signal processing.

The finite difference time domain (FDTD) method is widely used as a computational tool to simulate the electromagnetic wave propagation in biological tissues. When expressed in terms of Debye parameters, dispersive biological tissues dielectric properties can be efficiently incorporated into FDTD codes. In this paper, FDTD formulation with nonuniform grid is presented to simulate a dual medical implant communications service (MICS) (402-405 MHz) and industrial, scientific, and medical (ISM) (2.4--2.48\,GHz) band implantable antenna for continuous glucose-monitoring applications. In addition, we present computationally simpler two-pole Debye models that retain the high accuracy of the Cole-Cole Model for dry skin in MICS and ISM bands. The reflection coefficient simulation result with Debye dispersion is presented and compared with the published results. FDTD was also applied to analyze antenna's far-field.

In this paper, a novel beamformer for adaptive combination of two adaptive filters is proposed for interference mitigation of sensor array. The proposed approach adaptively combines two individual filters by coefficient weights vector instead of one scale parameter and takes the constraint of affine combination into consideration rather than previous studies. Due to the more degrees of freedom offered by the mixing vector, the proposed beamformer significantly improves the convergence and tracking performances of the combined filter under both stationary and non-stationary environments, respectively. Based on the generalized sidelobe canceller (GSC) structure, the optimal mixing vector is derived by Lagrange method, and then several new effective iterative algorithms are developed for its updating in practical implementation. Furthermore, theoretical discussions of the convergent performances and complexities of the proposed iterative algorithms are also investigated to verify the feasibility of the proposed beamformer. Moreover, the proposed methods in application of beamforming for interference mitigation of antenna array are simulated based space-time processing technique. When compared to existing methods, the proposed approach exhibits faster convergence rate and higher output signal to interference plus noise ratio (SINR). Its good behavior is illustrated through simulation results.

Information leakage of general input operations using button images in graphical user interface on touch screen monitors was experimentally investigated from images reconstructed by receiving the electromagnetic noise. In the experimental investigations for input operations of a personal identification number, it was confirmed that when a button image was touched, the touched button image can be identified from the reconstructed button images. This kind of information leakage has originated the fact that the touched button image has changed the color for informing the operator which button image was touched. From the elucidation of the image reconstruction mechanism, it was found that the information leakage has been caused by the magnitude of the emitted signal that results from the analog voltage differences of the RGB signals between neighboring pixels on the monitor. Therefore, a countermeasure method was proposed from the viewpoint of the combination of the colors of the button images and of the background or of the numerals in the button images. The countermeasure method was then applied to the previous input operations of a personal identification number. From the experimental results for the countermeasure method, it was confirmed that the touched button image cannot be identified from the reconstructed button image. As a result, the proposal countermeasure method can prevent effectively the information leakage of input operations on touch screen monitors due to the electromagnetic noise.

In this paper, we introduce a new non-uniform memory access (NUMA) acceleration algorithm for parallel finite-difference time-domain (FDTD) method on NUMA architecture workstation. We compare the performance of parallel FDTD method with and without the NUMA acceleration technique. An ideal test case and an engineering example show that the NUMA acceleration technique can efficiently improve the computing performance of FDTD parallel applications.